Where is the slytherin common room?

Ravenclaw Tower is located on the west side of Hogwarts, the staircase leading up to the common room is presumably located on the fifth floor, and is the location of the Ravenclaw common room and dormitories. The entrance to the room is at the top of a spiral staircase where it intersects with the rest of the castle.

The entrance itself is a wooden door with a golden eagle knocker on it. When you use the knocker, the eagle comes alive and asks a philosophical question which only a highly intelligent person will be able to answer. This is based on that Rowena Ravenclaw chose most intelligent students for her house so naturally she would want a place that only intelligent students could get in. But she may have felt that any intelligent student was worthy for her house despite not being admitted. This means that basically anyone who is intelligent enough can enter the Ravenclaw Common Room, as demonstrated when Minerva McGonagall enters the tower in 1998 at the order of Deputy Headmaster and Death Eater, Amycus Carrow.